Instrument for measuring impact strength of materials



Aug. 2, 1949.

C. R. STOCK INSTRUMENT FOR MEASURING IMPACT STRENGTH OF MATERIALS FiledNov 15, 1944 2 Sheets-Sheet 1 ATTORNEY 1949- c. R. sTocK 2,477,908

, INSTRUMENT FOR MEASURING IMPACT ATERIALS STRENGTH OF M 2 Sheets-Sheet2 Filed Nov. 15, 1944 7 N kw ATTORNEY Patented Aug. 2, 1949 T UFiF'I CEChafles R. zStnck, Greenwich, =Gonn., assigncr 1:0 American GyanamidCompany, .New York,

N. X, acorporation of Maine Am'rlicattion'Novem'ber 15, 1 94 1, 'Sclial'-No. 563;594

The qn esent smvention relates to a-"method :an'l

device jfomd'etermining Ashe energy required to a of fractu'rablematerial.

In this art many pro' iosals 'have been made for moducin'g :an impact ora known-force r on standardeshapedianc s'izetl sp'e'oimens of thematerial. Perhaps chemiost widelyaecepte-d sharpen-specimen is oneapprcxin'rately z' /g inches long, ap proximaitelyfl/ :inch wide andapproximately inch thick either "with er withcu't 'a netch at the centerthereof where the thiclcness or material ifrdm the bottom of th e notchtofi he opposite fa'ce ef the es app1=o ima;tely .-4 =ii1ch-. -Suh aespechnen when hlii for the inrpac't test in "a "cantileveredmannerislknown ash cantilevered specimen" by Qimerioan Society forTesting Materials; v

This form =oT specimen is particularly used Whereflt is dsiredtotleterniinethe*energy neces= sary *to fr'actnre such materials asresins, cera= hircs g lass andthe like. i y 7 instance; ewesm -wioe1used im act resting apparatus for deterniininig, the impact 6 Claims;(01. jar-412) strength of materials consists of a pendulum wmeh *lsallowed topsilhiteoh its 'aiiisgbeingreleased from a heig'htwmch willacclerate the striking edge to avelocityof about 12 feet per eecone atthe bottc'm of 'itssmne. "The impact takes place at the hottornof thearc. Such an annaratusfis cbjectionable in thatthemassjfofthe pendulumas restricted in several ways. For instance, it must be so distributedith'at'the center of mercussion substantially the same radius as thestriking edge and also "so that the kinetic available is (if the correctamountror 'lfili er the totalmass that the "center of percussion would:be sensiblyshilited away from the striking edge. this :range,:therefore, :a gpendulum pparatus :becomes unsatisfactory.

-Another :pXQpOSEI is to :use a so called guilleftine -method, \Whereinthe amass falls vertically, either freely 101 guided by rails, andstrikes :the snecimen from ithe Itop. :Here the energy range as(theoretically unlimited. since the center of gravity and the center aOfpercussion-can readily be, made coaxial. Where guide rails are used, thevelocity Bis erraticallyefiected, :from one test to the next, by thechance occurrence of sliding z'friction as the trailing weigh-t touchesthe rails vonzits way'down. :In both cases, whenlthe-specimen breaks itis extremely difficult, if not impossible, to measure the excess kineticenergy remaining in the weight and for this reason it has not been"attempted.

The principal "object of the present invention, itherefore, is $0determine the fracture energy required of a :moving striker where thekinetic energy '0f t-he striker before and after breaking the specimenmay :be readily and accurately c'alculated with minimum errors and"eliminating the human Zfactors.

vAna'other important object of the invention the accomplishment of theabove by means of a simple apparatus which Willbe of sturdy-construetion but readily flexible and adapted to ithe useeof strikers =of:difiereiit weight :mas'ses.

'To this encl=the-invention contemplates'fdevelom ingaa knownanflpredetermined. amount of-kinetic energy in :a supported sstriker,contactingthe striker'witha specimensand thereafter measuring reasonably(accurately the residual :and excess horizontalkinetic-energyremaininginthe'striker. The clifierenoe between these two"factors is the .energyrequired :to fracture the specimen.

A convenient Way of accomplishing xthe above is too-permit a ball ofknown weightto roll an incline, the end. portion of which causes theball to have .a horizontal end run. At .the =time the hall reaches theend of the run way,.it should have acquired energy slightly greater thanthat required to fracture'the specimen. At that point the specimenfisstruck the striker, the former broken and. 'theball continues (itsJflight in a ,parabolic curve until it strikes a horizontal surface.This surface is of -a character which will record the point or contactof the'ball therewith so that the horizontal distance travelled by theball after breaking the specimen may be measured. Knowing the height ofthe point of contact between the ball and the specimen above thehorizontal surface and the horizontal kinetic energy of the ball at thetime of impact with the specimen it becomes a simple mathematicalproblem to calculate the energy absorbed in breaking the specimen.

In this proposal the advantages of a pendulum and a guillotine areretained while avoiding the objectionable features thereof. Thusacceleration is produced by the vertical operation ofthe force ofgravity, but the direction of the accelerated striking mass is changedto the horizontal for the impact. This change of direction is notproduced by an arm suspension which is part of the mass and which,therefore, effects its dynamics as in the case of a pendulum, but ratherby guide rails which support the striker from below and do not affectits relationship of center of percussion to point of impact. g Since thedirection of the mass is presumably horizontal as it leaves its run way,its path at any time during free fall will be a parabolic arc themathematical relations of which permit the ready measurement of thehorizontal component of velocityand, therefore, the horizontaltranslational kinetic energy. Such a proposal has the advantage over theguillotine method in that contact of the striker with its guide rails isa constant which may be taken into consideration and it is a simplematter to determine the residual and unopposed kinetic energy of thestriker.

The invention further includes a device for accomplishing the abovepurpose which may take the-form of guide rails arranged at someconvenient angle between the horizontal and vertical so as to obtain thedesired gravitational acceleration of the striker, the guide rails orother supporthaving a horizontal end run so as to project the strikertherefrom in-a horizontal direction. A vice or structure is provided forholding the specimen in the path of the striker whenpro- J'ected fromits horizontal end run. A record sheet is arranged on ahorizontalsurface beneath and beyond the specimen having a point of referenceverticall below the point of contact between the striker and thespecimen. This record sheet may be calibrated according to well knownmathematical. formulas and subdivisions with reference lines placedthereon to indicate where a striker will fall after breaking a specimenandhaving any residual amount of its total horizontal kinetic energy.Thus the minimum andlmaximum points of reference on .therecord sheetwould be that at which allof the'horizontal kinetic energy developed bythe striker is absorbed in fracturing the specimen and the strikerthereafter would fall vertically therefrom. The maximum point ofreference on the record would be that point at which the striker wouldcontact therewith if no specimen interfered with itsparabolic flightfrom the end of the run way. This last point of reference wouldrepresent unity or that the striker at that point contained 100%horizontal kinetic energy. Any suitable 'number of graduations may bemade between the minimum and maximum points of reference so as to readdirectly in terms of the horizontal kinetic energy absorbed in breakingthe specimen. It is' preferable that such a record sheetbe covered withsome material such as carbon paper sothat when the striker falls thereonit will leave an imprint on the record to mark its point of contact.

The invention further includes the novel construction, combination andarrangement of parts and the manner of use as more fully hereinafterpointed out in the description and shown in the drawings.

In the drawings:

Fig. 1 is a side elevation of the device constructed according to theinvention.

Fig. 2 is a front view of the device of Fig. 1.

Fig, 3 is a plan view-of the device of Fig. 1.

. Fig. 4 is a sectional view along the line 4-4 of Fig. 1.

Fig. 5 is a detail showing the striker-carbon paper-record sheetcombination along the line 5-5 of Fig. 3.

Referring now to the drawings, a base is shown at l carrying an inclinedsupport 2 having parallel guide rails 3 adapted to support a strikerwhich in this case is ball 4. Any desired form of striker may be usedwhich may be gravitationally accelerated and which ma have an accuratepoint of contact not only with the specimen but with the horizontalsurface after breaking the latter. Aballis the most'convenient form ofstriker;

A cradle 5 pivotedjas at 6 may be made to hoIdthe striker {until readyfor use andreleased for its run by the operation of trigger L,

The major portion of therunway constituted by; rails 3 may be arrangedat any angle between the horizontal and thevertical terminating in acomparatively short horizontal end run 8.

A l s o carried by the base Iris a vice for holding the specimen in acantilevered manner. This may include a bracket s carrying a clamp l0mounted for vertical sliding motion on the bracket 9 and adjustable toany desired vertical position by means of screw I I which bears thereeeensiand Operated 1h wh e The amping w t-P ma. a to receive a sp im I3 ofthe material undergoing test, the specimen being held within the clampby reason of screw 'l4 and knurledknob [5. The specimen may, therefore,beadjusted vertically so as to assure impact of the striker therewith'at the correct point. Other suitable structures may be -substituted forholding specimens which are tobe fractured other "than as cantilevers,such as doubly supported simple beams. It is to be'noted that'tliere isa spacbetween'the end of the perimeter portion o'f'the rails 3 and thenear face'of "the specimen l3." The dimensions of this spacefslio'uld begreater'thaii the larger dimensiorf'of' thefstrikensofthat in the eventthat the horizontal kinetic "energy developed by the striker'at'thej'time' of impact with the specimen is equal t'o'or'less than thati'eqliiredto break the specimen the striker may mov'downwardly throughthis space and toward'the' record sheet. Beneath the" specimenis'ahorizontal surface having corner guides"lfi'arranged to receive 'arecord sheet 11 inthe"de'siredposition. O'n'the record sheet aredrawnreference lines IS the position of which willbehe'reinafter'jdescribed.

Overlying the record sheet I! is apiece of carbon paper l9 sothat'when'the striker '4 leaves the end of 'the rails 3 and performs itswork and drops "onto the I horizontal surface beneath 'the specimenjitspoint of contact will be recorded on' the recordsheet' "in a visualmanner.' f 'Twelve' steerban strikers co'fnpri's'ing a "s't varying inweight" convenient steps were o'rated on area 'way'at mangl ofapproximately Variation of Energy,

V. (in percent) it??? Energy,

Sec.

Diameter,

Ft. Lbs.

Weight, inches Pounds The mathematical formula for determining thegraduations on the record sheet I1 and also for determining the amountof energy required to fracture a given specimen is as follows:

L ll x s +1 in which:

E1 is the total kinetic energy of the striker before fracture ofspecimen.

x1 is the horizontal distance from the end of the support to the pointof impact of the striker with the horizontal surface when the flight ofthe striker is unimpeded.

x2 is the horizontal distance from the point of impact between thestriker and the specimen and the point of contact between the Strikerand the horizontal record after breaking a specimen.

s is the distance between the end of the striker support and the impactface of a specimen.

r is the radius of a ball striker.

While the invention has been described with particular reference tospecific embodiments, it is to be understood that it is not to belimited thereto but is to be construed broadly and restricted solely bythe scope of the appended claims.

What is claimed is:

1. A device for determining the energy required to fracture acantilevered specimen of fracturable material which includes a striker,a

Absorbed energy: E {1 supporting runway therefor the major portion ofwhich is arranged at an angle between the horizontal and the vertical,said runway having a horizontal end run, a vice for holding a specimenin the path of the striker when projected from the horizontal end run ofthe runway, and means for determining the residual horizontal kineticenergy of the striker after it fractures the specimen.

2. The device of claim 1 in which the runway includes parallel guiderails.

3. The device of claim 1 in which the vice is spaced from the horizontalend run of the runway a distance greater than the greatest dimension ofthe striker.

4. The device of claim 1 in which the vice is provided with means forvertical adjustment of the specimen.

5. The device of claim 1 in which the means for determinin the residualhorizontal kinetic energy of the striker after it fractures the specimenincludes a horizontal record a known distance below the specimen andcontaining graduations indicating the portion of kinetic energy of thestriker absorbed in fracturing the specimen.

6. The device of claim 1 in which the means .for determining theresidual horizontal kinetic energy of the striker after it fractures thespecimen is a horizontal record sheet a known distance below thespecimen and containing graduations indicating the portion of kineticenergy of the striker absorbed in fracturing the specimen, said recordsheet being overlaid with a carbon sheet so that upon contact of thestriker with the carbon sheet a visual record of the contact will appearon the record sheet.

CHARLES R. STOCK.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS FOREIGN PATENTS Country Date Switzerland Mar. 16,1928 Number Number

